High resolution functional analysis and community structure of photogranules

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Ecosystem Science

Background:

• Photogranules are microbial aggregates with potential for sustainable, aeration-free wastewater treatment.
• Understanding their internal structure and biogeochemical processes is crucial for optimizing their application.

Purpose of the Study:

• To elucidate the composition, stratification, and nutrient cycling within photogranules.
• To determine the budgets of light, carbon, and nitrogen within these microbial ecosystems.

Main Methods:

• Fluorescence microscopy and 16S/18S rRNA gene amplicon sequencing for composition analysis.
• Microsensors and stable/radioisotope incubations for nutrient and gas flux measurements.

Main Results:

• Photogranules exhibit distinct biological and chemical stratification, with cyanobacteria forming a structural scaffold.
• Oxygen, nitrate, and light gradients were observed, with photosynthesis and nitrification concentrated in the outer 500 µm.
• Internal cycling of oxygen, nitrogen (nitrification-denitrification), and carbon (photosynthesis-respiration) was balanced.

Conclusions:

• Photogranules function as complete, self-sustaining ecosystems with intricate, linked nutrient cycles.
• These findings provide critical insights for the engineering and design of photogranular wastewater treatment systems.